Process for pyrolysis of glycerol-containing feedstocks

ABSTRACT

A process and apparatus for producing a hydrogen-containing product gas ( 4 ) from a glycerol-containing feedstock ( 1 ). A product gas ( 4 ) is produced from the glycerol-containing feedstock ( 1 ) by separation of undesirable substances (V) and the pyrolysis of glycerol (P).

The invention relates to a process for producing a hydrogen-containing product gas (product gas) from a glycerol-containing feedstock as well as a device for implementing the process.

In an attempt to reduce the introduction of carbon dioxide into the earth's atmosphere or at least to not let it increase further, and as alternatives to the dwindling natural oil and natural gas reserves, energy sources in enhanced form will be produced in the future from renewable raw materials. According to an EU guideline, at least 5.75% of the fuel requirement is to be covered by such energy sources in the European Union until 2010. In this connection, biodiesel, which even now is added at a concentration of up to five percent to the diesel fuel available at German gas stations, plays a tremendous role.

Biodiesel is a standardized fuel that is obtained from, e.g., rapeseed oil but also from other plant oils and fats. Plant oils and fats consist of triglycerides, i.e., fatty acid tri-esters of glycerol. This structure causes plant oils and fats to be viscous to solid at normal ambient temperatures, i.e., to have a much higher viscosity than the fuels for which a commercially available diesel engine is designed. Plant oils and fats behave differently in the injection process, and also the combustion proceeds less cleanly. These drawbacks can be only incompletely compensated for even by motor-driven interventions—such as, for example, preheating the plant oil.

Biodiesel is produced from plant oils and fats by the replacement of glycerol by methanol. Its viscosity corresponds to that of commercially available diesel fuel, which is why it can be easily consumed even in unmodified diesel engines.

The glycerol that is separated from the plant oils and fats in the biodiesel production is not obtained in pure form but rather accumulates as a portion of the mixture of materials, which contain larger amounts of contaminants in addition to glycerol. Such a mixture of materials is, for example, so-called crude glycerol, which has a glycerol content of 80-85%, but in addition also contains water, salts e.g. potassium salts, and organic contaminants (e.g., fatty acids or methanol) as well as residues from the production process in still larger amounts. According to the prior art, the crude glycerol is purified in expensive process steps by vacuum distillation, deodorizing and filtration, to the extent that it is sufficient for the strict requirements of the European Pharmacopeia and can be sold to the pharmaceutical industry with a purity of at least 99.5% as a pharmaceutical glycerol. At present, the entire amount of glycerol that accumulates in the biodiesel production can be used in this way. With the foreseeable expansion of the biodiesel production, this will be increasingly more difficult in the future, however, so that other ways of using crude glycerol must be sought.

It is therefore the object of the invention to provide a process of the above-mentioned type as well as apparatus for implementing the process, which make it possible to direct glycerol-containing by-products that accumulate in biodiesel production to a productive use.

This object is achieved according to the process side of the invention in that a product gas is produced from the glycerol-containing feedstock by separation of undesirable substances and pyrolysis of glycerol.

In this connection, pyrolysis is defined as the thermal decomposition of glycerol in volatile molecules, whereby the decomposition is carried out with the exclusion of oxygen and water or—deviating from the usual definition—in the presence of oxygen and/or water.

The invention is based on the experience that when glycerol-containing feedstocks, such as, for example, crude glycerol, are put to direct use by gasification, problems arise—which cannot be overcome or can be overcome only at great expense—owing to the high proportion of contaminants that are present in the feedstocks. Thus, salts lead to corrosion of system parts. Also, organic contaminants are controlled only with difficulty and can result in deposits and the formation of carbon black.

One embodiment of the process according to the invention calls for the separation of undesirable substances—already present in the feedstock and/or produced in the implementation of the process according to the invention—and the pyrolysis of glycerol to be implemented simultaneously in one process step.

Another embodiment of the process according to the invention calls for a product gas to be obtained from the feedstock in at least two successive process steps, whereby in each of the process steps, undesirable substances are separated and/or glycerol is reacted by pyrolysis.

To separate undesirable substances that are present in the feedstock, the feedstock according to the invention is preferably subjected to a distillation and/or a thermal drying and/or a filtering on activated carbon and/or a membrane and/or chromatography and/or an ion exchange and/or an ion exclusion and/or a precipitation.

In a suitable way, the water or steam content in the glycerol-containing fraction that was recovered by separating undesirable substances from the feedstock is set at a value by adding or removing water or steam, which makes it possible to implement a subsequent pyrolysis without the formation of carbon black and with simultaneously minimum energy input.

Another embodiment of the process according to the invention calls for the water required for pyrolysis to be fed in more than one step (in a stepped process), whereby the water is fed before and/or during pyrolysis at a suitable location. If pyrolysis is implemented in several successive steps (pyrolysis steps), it is useful for water to be added in each case before a pyrolysis step.

If the glycerol-containing fraction is fed in liquid form to pyrolysis, water is preferably fed in the form of steam, whereby the steam is sprayed into the glycerol-containing fraction or the glycerol-containing fraction is sprayed into the steam. A portion of the energy required for the subsequent pyrolysis is already introduced with the steam, which results in a reduced heating expense in the pyrolysis reactor and in a reduction of the equipment cost for the pyrolysis reactor.

Since it is possible to pressurize, at low cost, the glycerol-containing fraction in liquid form and to conduct pyrolysis at an increased pressure, the process according to the invention is suitable in particular for producing a product gas under increased pressure. Thus, an expensive compression of the product gas can be eliminated.

In this connection, thermal drying is defined as the feedstock being introduced into a thermal drying system and being subjected there to a thermal treatment. Volatile components, such as water and glycerol, are evaporated and form a gas fraction possibly with other gaseous substances, while solids, such as, for example, salts, are converted into a largely anhydrous solid fraction. Solid and gas fractions are then separated to a large extent from the thermal drying system, which is equipped for this purpose with a suitable system for separating dust and gas, such as, for example, a gravity separator and/or a cyclone and/or a filtering system and/or a water scrubber.

At sufficiently high temperatures, glycerol is thermally decomposed, i.e., pyrolyzed into a gas containing hydrogen. Further developing the process according to the invention, it is therefore proposed that the thermal drying of the feedstock be implemented at temperatures in which at least part of the glycerol contained in the feedstock is pyrolyzed. Depending on how much of the glycerol is pyrolyzed in the thermal drying, the gas fraction is subjected to further pyrolysis downstream of the thermal drying.

An advantageous embodiment of the process according to the invention calls for the heat that is required for thermal drying of the feedstock to be removed from the hot product gas.

Preferably, for thermal drying of the feedstock, fluidized-bed granulators and/or fluidized-bed dryers and/or drum dryers and/or fluid-bed dryers and/or suspension dryers and/or paste dryers are used.

Variants of the process according to the invention call for the pyrolysis to be implemented while water and/or steam and/or an oxidizing agent are being fed in, whereby the oxidizing agent is air or oxygen-enriched air or oxygen.

The application of oxygen during the pyrolysis step refers to another reaction option. The glycerol will react partly with the oxygen to steam and CO/CO₂. The benefit is the internally generated heat which is used for the pyrolysis of the remaining glycerol. This results in decreased operating costs owing to an improved heat transfer/balance. This variant will lower the requirement of energy from the externally applied heat (usually methane) but will use some of the glycerol and the applied oxygen to form CO/CO₂.

Based on the process, which is selected for separating undesirable substances from the feedstock, an aqueous mixture (waste water), in which the separated substances are present in dissolved and/or suspended form and whose material cannot be used without additional treatment, can accumulate when the process according to the invention is implemented. The waste water represents a waste that has to be shipped to a hazardous waste site at a dump. To keep dumping costs low, an attempt is made to keep the volume of waste to be dumped as small as possible. An embodiment of the process according to the invention therefore calls for the waste water to be subjected to a treatment in which the volume of waste to be deposited is reduced. The waste water is preferably subjected to drying in a thermal drying system, whereby a largely anhydrous solid fraction and a gas fraction are produced. In the most advantageous case, the thus obtained solid fraction can be used economically (e.g., as fertilizer), so that the volume of waste to be dumped drops to zero.

An advantageous embodiment of the process according to the invention therefore calls for the heat that is required for thermal drying of waste water to be removed from hot product gas. Based on the heat that is released from the hot product gas to the waste water, volatile components pass from the waste water into the gas phase, by which a gas fraction and a largely anhydrous solid fraction—which is present, for example, as a granulate or powder depending on the drying process that is used—are produced.

The hot gas stream that is used for thermal drying of waste water is a part of the product gas, and its heat is transferred in direct heat exchange to the waste water to be dried, thus a further development of the process according to the invention calls for the gas fraction that is produced during drying to preferably be subjected to a water scrubbing system of a water scrubber and then be recycled before pyrolysis. In a suitable way, the charged scrubber water is drawn off from the water-scrubber system and mixed in with glycerol-containing feedstock.

For thermal drying of waste water, fluidized-bed granulators and/or fluidized-bed dryers and/or drum dryers and/or fluid-bed dryers and/or suspension dryers and/or paste dryers are preferably used.

The invention also relates to a device for implementing the process according to the invention.

In terms of the device, this object is achieved in that it comprises a pyrolysis system in which a product gas can be produced from the feedstock by separation of contaminants and pyrolysis of the glycerol contained in the feedstock.

A preferred embodiment of the device according to the invention calls for the pyrolysis system to consist of a thermal drying system, in which a gas-free and largely anhydrous solid fraction can be produced from the feedstock, whereby based on the temperatures prevailing in the thermal drying system, glycerol that is present in the gas fraction is at least partially pyrolyzed. In a suitable way, the thermal drying system comprises a suitable system for separating dust from the gas fraction, so that a largely dust-free product gas can be produced. Preferably, the thermal drying system is a fluidized-bed granulator and/or a fluidized-bed dryer and/or a drum dryer and/or a fluid-bed dryer and/or a suspension dryer and/or a paste dryer. Such thermal drying systems have been known to one skilled in the art for many years and are available on the market.

Another preferred embodiment of the device according to the invention calls for the pyrolysis system to comprise a purification system and a downstream pyrolysis reactor, whereby a prolysis feedstock, which can be reacted into product gas in the pyrolysis reactor by pyrolysis, can be produced in the purification system from the feedstock by separation of contaminants. According to the invention, the purification system is preferably designed as a vacuum distillation system and/or a thermal drying system and/or a filtering system with activated carbon or membrane and/or a chromatography system and/or an ion exchanger and/or an ion exclusion system and/or a precipitating and separating system.

A suitable embodiment of the device according to the invention calls for a suitable system with which the water or the steam content of the glycerol-containing fraction—obtained by separation of undesirable substances from the feedstock—can be adjusted preferably to a value that is advantageous for implementing a subsequent pyrolysis by adding or removing water or steam.

Another embodiment of the device according to the invention calls for a suitable system with which the water that is required for pyrolysis can be fed to a suitable location in front of the pyrolysis reactor and/or in the pyrolysis reactor in more than one step (in a stepped process). If the pyrolysis is implemented in several pyrolysis reactors that are arranged in series, water can be fed in each case in front of a pyrolysis reactor in a useful way.

If the glycerol-containing fraction is fed to the pyrolysis system in liquid form, the device according to the invention preferably comprises a system for mixing steam with the glycerol-containing fraction (mixer), whereby steam can be injected into the glycerol-containing fraction or the glycerol-containing fraction can be injected into the steam. In an attempt to design the mixer as compactly as possible, a nozzle—via which the glycerol-containing fraction is sprayed as a fine mist into the greatly turbulent steam—is provided, for example, at a suitable location. A portion of the energy required for the subsequent pyrolysis is already introduced with the steam, which results in a reduced heat demand in the pyrolysis reactor and in a reduction of the equipment cost for the pyrolysis reactor.

An advantageous variant of the device according to the invention calls for a system for reducing the water content of an aqueous mixture (waste water) whose material cannot be further used and that accumulates when the glycerol-containing feedstock is purified. Preferably, this system is a thermal drying system, such as, for example, a fluidized-bed granulator and/or a fluidized-bed dryer and/or a drum dryer and/or a fluid-bed dryer and/or a suspension dryer and/or a paste dryer. Such thermal drying systems have been known to one skilled in the art for years and are available on the market, by such companies as GEA Barr-Rosin, ALL GAIER and FIMA, for example. In a suitable way, the thermal drying system is designed so that a largely anhydrous solid fraction and a largely dust-free gas fraction can be produced from the waste water.

The thermal drying system is a system in which energy can be fed to the waste water to be dried in direct contact with hot product gas; thus, an advantageous embodiment of the device according to the invention calls for a water scrubbing system into which the dust-charged gas stream that exits from the thermal drying system can be introduced and freed from dust there by water scrubbing before it is recycled and fed to the pyrolysis reactor as feedstock. In a suitable way, the charged scrubbing water can be removed from the water scrubber and mixed in with the crude glycerol.

BRIEF DESCRIPTION OF DRAWING

Below, the invention is to be explained in more detail based on a non-limiting preferred embodiment that is depicted diagrammatically in the FIGURE:

This embodiment relates to a unit for producing a product gas, whereby crude glycerol from the biodiesel production is used as a feedstock.

Via line 1, the crude glycerol is introduced into the vacuum distillation system V, where it is separated into two streams 2 and 3. Then, the stream 2, which consists almost exclusively of evaporated glycerol, is sent to the pyrolysis reactor P as a feedstock and is converted there to a hydrogen-containing product gas, which is drawn off via line 4 from the pyrolysis reactor P. Stream 3 from the vacuum distillation system V, which consists primarily of water and salts, as well as residues from the biodiesel production, is sent to the granulator G and dried there by means of a part 5 of the hot hydrogen-containing product gas 4. The salts and other solids contained in stream 3 are converted into a granulate and drawn off via line 6 from the granulator G. Via line 7, a stream, which consists primarily of gases and vapors, but in addition also contains solids in dust form, is fed to the water scrubbing system W and purified there. A part of the charged scrubber water from the water scrubbing system W is drawn off via line 8 and introduced together with the crude glycerol via line 1 into the vacuum distillation system V, while the other part 9 is mixed with fresh water 10 and is recycled as scrubbing water in the water scrubber system W. Via line 11, a stream that consists largely of product gas and steam is drawn off from the water scrubber system W and fed together with the glycerol stream 2 to the pyrolysis reactor P.

As compared to the above described embodiment in a one-step process, the crude glycerol is heated up to a temperature high enough to evaporate glycerol, and hence separate it from the impurities, and simultaneously crack the glycerol molecules in a pyrolysis reaction.

Conversely, the first step of the two-step process is a purification step, in which glycerol is mainly evaporated, in order to separate it from impurities. Whether pyrolysis takes place in the purification step depends on the applied temperature within the purification. If the temperature is high enough, the pyrolysis of glycerol starts in the purification step.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

The entire disclosures of all applications, patents and publications, cited herein and of corresponding German application No. 10 2007 060 166.4, filed Dec. 13, 2007 are incorporated by reference herein.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. 

1. A process for producing a hydrogen-containing product gas (4) from a glycerol-containing feedstock (1), containing impurities, comprising the steps of (a) separating the impurities from the glycerol-containing feedstock (1) and (b) subjecting the resultant glycerol (P) to pyrolysis to produce a hydrogen-containing product gas.
 2. A process according to claim 1, wherein the step of separating of impurities present in the feedstock and/or produced during the process and the step of pyrolysis of glycerol are conducted simultaneously in one process step.
 3. A process according to claim 1, wherein the product gas (4) is obtained from the feedstock (1) in at least two successive process steps, whereby in each of the process steps, impurities are separated and/or glycerol is reacted by pyrolysis.
 4. A process according to claim 1, wherein the pyrolysis (P) is conducted with water and/or steam and/or an oxidizing agent wherein the oxidizing agent is air or oxygen-enriched air or oxygen.
 5. A process according to claim 1, wherein impurities present in the feedstock (1) are separated by distillation (V) and/or thermal drying and/or filtering on activated carbon and/or membrane and/or chromatography and/or ion exchange and/or ion exclusion and/or precipitation.
 6. A process according to claim 5, comprising the thermal drying of the feedstock, said thermal drying being conducted at temperatures sufficient to cause at least a partial pyrolysis of the glycerol contained in the feedstock (1).
 7. A process according to claim 1, wherein an aqueous mixture (3) accumulates during the separating of impurities from the feedstock (1) in which the separated impurities are present in dissolved and/or suspended form, and subjecting the aqueous mixture to drying in a thermal drying system (G), to obtain a largely anhydrous solid fraction (6) and a gas fraction (7).
 8. Apparatus for producing a hydrogen-containing product gas (4) from a glycerol-containing feedstock (1), comprising means for separating from the feedstock by contaminants from a feedstock and means for subjecting resultant contaminant-depleted feedstock containing glycerol to pyrolysis (P) of the glycerol.
 9. Apparatus according to claim 8, wherein the pyrolysis system comprises means for thermal drying of the feedstock, in which a gas-free and a largely anhydrous solid fraction can be produced from the feedstock, whereby glycerol that is present in the gas fraction is at least partially pyrolyzed based on the temperatures prevailing in the thermal drying means.
 10. Apparatus according to claim 8, wherein the pyrolysis system comprising purification means (V) and a downstream pyrolysis reactor (P), whereby a pyrolysis feedstock (2) can be produced in the purification system from the feedstock (1) by separation of contaminants and can be reacted in the product gas (4) in the pyrolysis reactor (P) by pyrolysis.
 11. Apparatus according to claim 8, wherein the purification means (V) comprises a vacuum distillation system and/or a thermal drying system and/or a filtering system with activated carbon or membrane and/or a chromatography system and/or an ion exchanger and/or ion exclusion system and/or a precipitation and separation system.
 12. Apparatus according to claim 8, wherein comprising means (G) for reducing the water content of waste water comprising material that accumulates when the glycerol-containing feedstock (1) is purified.
 13. A process according to claim 1, comprising providing a crude glycerol feed containing salt impurities from a transesterification reaction subjecting said crude glycerol feed to a distillation so as to provide an overhead of purified glycerol and a bottoms of a liquid waste product containing salts subjecting the purified glycerol to pyrolysis so as to obtain a hydrogen-containing product passing the liquid waste product containing salts from the distillation to a fluidized bed granulator branching a stream of pyrolyzed glycerol containing hydrogen into said granulator so as to provide heat for drying, and withdrawing from said granulator granulated salts and a stream comprising dust and primarily gases, and scrubbing the stream comprising dust and primarily gases with water so as to provide a water stream containing said dust as a bottoms product and an overhead comprising mostly pyrolysis gas and steam. 